A marine nitrogen oxide reducing agent and a method for preparing the same

Abstract

The application discloses a kind of ship nitrogen oxide reducing agent and preparation method thereof, belong to ship nitrogen oxide reducing agent technical field, the preparation method includes: hydrolytic crystallization, dissolves, filters, fine filters, ultrafiltration;The hydrolytic crystallization, after mixing industrial urea and tertiary water, stirring is carried out at 73-75 DEG C, first cooling is carried out, dodecyn diol polyoxyethylene ether is added, second cooling is carried out, mixed urea solution with temperature of 62.5-64 DEG C is added, third cooling is carried out, insulation, centrifugal, and the precipitate is collected;The application is produced using the same production equipment as automobile nitrogen oxide reducing agent to produce ship nitrogen oxide reducing agent, film pollution problem is not prone to appear in production, production efficiency is high, production input cost is less, production energy consumption is small, and the prepared ship nitrogen oxide reducing agent meets standard requirements.

Description

Technical Field

[0001] This invention relates to the field of nitrogen oxide reducing agents for ships, and specifically to a nitrogen oxide reducing agent for ships and its preparation method. Background Technology

[0002] Nitrogen oxides (NOx) are major contributors to environmental damage and acid rain formation, and they also harm human health. Statistics show that ships globally emit approximately 10-15 million tons of NOx annually, accounting for a significant proportion of total global NOx emissions, roughly 7-14%. In light of this, the International Maritime Organization (IMO) and the Chinese government are increasingly emphasizing the problem of NOx pollution from ships and are continuously raising the requirements for controlling NOx emissions from vessels.

[0003] The International Convention for the Prevention of Pollution from Ships (ICP-1) is an international convention established by the International Maritime Organization (IMO) to protect the marine environment and to provide safety regulations for preventing and limiting the discharge of oil and other hazardous substances from ships into the ocean. Currently, relatively mature single technologies that meet the Phase III ammonia oxide control standards stipulated in Annex VI of the ICP-1 include: Selective Catalytic Reduction (SCR) technology, Exhaust Gas Recirculation (EGR) technology, and Low-Pressure Injection Liquefied Natural Gas (LNG) engine technology. Among these, SCR technology has a wide range of applications and minimal impact on engine safety, gaining widespread industry recognition, and an increasing number of shipping companies are choosing to install SCR systems on the fuel engines of newly built ships.

[0004] SCR (Selective Catalytic Reduction) technology is an exhaust gas aftertreatment technology based on the selective reduction reaction of a reducing agent with nitrogen oxides in exhaust gas, converting them into harmless nitrogen and water. SCR technology is the mainstream technology for reducing harmful nitrogen oxides in diesel engine exhaust and is an essential system for ensuring that modern automobiles and ships strictly comply with emission regulations. Urea aqueous solution has the advantages of being safe, non-toxic, easy to store, and convenient to prepare, and is widely used in SCR systems for automobile and marine diesel engines. When the mass fraction of urea in the urea aqueous solution is 32.5%, the crystallization temperature of the urea aqueous solution is the lowest, at -11℃. To avoid crystallization at low temperatures and to facilitate the injection of the urea aqueous solution into the exhaust pipe at low temperatures, the nitrogen oxide reducing agent used in automobile diesel engine SCR systems is mainly a 32.5% mass fraction urea aqueous solution. Because marine diesel engine SCR systems require a larger amount of reducing agent, and the temperature in the ship's engine room is high, making crystallization less likely, the nitrogen oxide reducing agent used in marine diesel engine SCR systems is mainly a 40% mass fraction urea aqueous solution.

[0005] To regulate the market for marine nitrogen oxide reducing agents, my country issued GB / T 35176.1-2017 / ISO 186 11-1:2014 Ships and Marine Technology - Marine Nitrogen Oxide Reducing Agents AUS 40 on December 29, 2017, and implemented it on July 1, 2018. This standard designates the nitrogen oxide reducing agent used in marine SCR systems as "Marine Nitrogen Oxide Reducing Agent AUS40" and specifies its urea content, density at 20°C, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble matter content, phosphate content, calcium content, iron content, magnesium content, sodium content, and potassium content.

[0006] As a manufacturer of automotive nitrogen oxide reducing agent (a urea aqueous solution with a mass fraction of 32.5%), the applicant, considering that both automotive and marine nitrogen oxide reducing agents are high-purity urea aqueous solutions, with the main difference being that the mass concentration of urea in the high-purity urea aqueous solution is increased from 32.5% to 40%, uses the same production equipment as the automotive nitrogen oxide reducing agent and refers to the preparation method of the automotive nitrogen oxide reducing agent. First, the industrial urea is purified by hydrolysis and crystallization to remove water-soluble impurities. Then, a 40% urea aqueous solution is obtained by dissolving the urea in tertiary water. The solution is then filtered sequentially using a polyethylene filter, a polypropylene filter, and a polysulfone membrane to remove insoluble impurities, thus obtaining the marine nitrogen oxide reducing agent. However, based on the publicly available information in "Thoughts and Suggestions on Developing New Business of Marine Nitrogen Oxide Reducing Agents" (Zhu Zongmin, *China Petroleum Enterprises*, May 2020), from a production and operation management perspective, automotive nitrogen oxide reducing agents and marine nitrogen oxide reducing agents are two completely different types of products for users. When the applicant, following the above method, made simple adjustments to the preparation method on the original production equipment to prepare marine nitrogen oxide reducing agents, the following problems were encountered: Question 1: In purifying industrial urea through hydrolysis crystallization, the applicant referenced the content published in "Research on the Preparation of High-Purity Automotive Urea by Cooling Crystallization" by Li Pan, Dalian University of Technology, June 2017. In cooling crystallization, a rapid cooling rate can lead to the preservation and adsorption of impurities in the liquid, resulting in urea crystals with a large aspect ratio and small size, which is detrimental to downstream processes. Therefore, a slow-then-fast cooling method was adopted: a slow cooling rate of 0.05℃ / min for the first 100 minutes, followed by a cooling rate of 0.10℃ / min for 70 minutes, and finally a rapid cooling rate of 0.20℃ / min for 40 minutes. The stirring speed was set to 300 rpm during the cooling process. However, in this route, increasing the cooling rate in the later stages makes the solution system unstable and prone to nucleation, and increases supersaturation, promoting secondary nucleation. This results in an increased number of urea crystals with small crystal size and uneven particle size. Because the production of nitrogen oxide reducing agents for automobiles is not continuous, after obtaining urea crystals through cooling crystallization, the urea crystals are temporarily stored. However, according to the published article "Causes and Solutions for Urea Product Agglomeration" by Li Tongsheng in *Guangdong Chemical Industry*, April 1991, if the urea particles are uniform and of appropriate size, dust entrainment in the product can be reduced. Therefore, if the obtained urea crystal particles are not uniform and contain a large number of small-sized urea particles, dust entrainment is more likely to occur, further leading to a high content of insoluble matter in the urea aqueous solution prepared from urea crystals. According to the published article "Research on High-Efficiency Concentration of Urea Aqueous Solution by Multi-Effect Membrane Distillation" by Zhang Lili in *Tianjin University*, June 2012, the membrane flux of the ultrafiltration module decreases after a period of time, causing membrane fouling. Especially with the increase of urea content in the urea aqueous solution and the relative dust content in the urea crystals used, membrane fouling is more likely to occur in ultrafiltration.

[0007] To address this issue, after research, the most commonly used methods are: Method 1: Based on the research on the preparation of high-purity automotive urea by cooling crystallization, published by Li Pan, Dalian University of Technology, June 2017, a slow cooling route is adopted, that is, the cooling rate is controlled at 0.05℃ / min and the stirring speed is 300rpm, so as to obtain urea crystals with large crystal size and uniform particle size. However, due to the extended cooling time, the production efficiency will decrease.

[0008] Method 2: Based on the research on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation. Zhang Lili. Tianjin University. June 2012, in order to avoid membrane fouling, a membrane material with strong hydrophilicity and a membrane surface charge consistent with the solute charge in the solution can be selected according to the properties of the feed solution. However, changing the membrane material involves equipment modification, which leads to an increase in production input costs.

[0009] Question 2: According to the research on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation, published by Zhang Lili, Tianjin University, June 2012, urea viscosity increases with increasing urea concentration. Furthermore, the relative content of insoluble matter in the urea aqueous solution also increases with increasing urea concentration. However, according to the research progress on the causes and model characterization of ultrafiltration membrane fouling, published by Chen Anwen and Shi Xiangyun, Guangdong Chemical Industry, September 2012, increased viscosity affects mass transfer efficiency, increases the surface resistance of the ultrafiltration membrane, and reduces membrane flux. Furthermore, the increase in the relative content of insoluble matter also exacerbates membrane fouling problems in ultrafiltration.

[0010] To address this issue, a search revealed that the most commonly used method is based on the research on high-efficiency concentration of urea aqueous solution using multi-effect membrane distillation. This is described in Zhang Lili's article, *Research on High-Efficiency Concentration of Urea Aqueous Solution by Multi-Effect Membrane Distillation*, Tianjin University, June 2012. Increasing the ultrafiltration temperature reduces the viscosity of the urea aqueous solution, but this leads to increased energy consumption. Alternatively, viscosity-reducing modifiers can be added to the urea aqueous solution. However, according to the research in *Preparation and Performance Testing of Organic Amine-Type Low-Temperature Diesel Vehicle Urea Solution*, Wu Xiaoman, Wang Weiyi, Xing Lijun, Shi Ruonan, *Journal of Xuchang University*, August 2018, commonly used modifiers such as small-molecule alcohols increase the viscosity of the urea aqueous solution, further exacerbating membrane fouling. Other modifiers not only pose safety concerns but may also affect the refractive index of marine nitrogen oxide reducing agents, further causing the prepared marine nitrogen oxide reducing agents to fail to meet the refractive index requirements in GB / T 35176.1-2017 / ISO 186 11-1:2014 Marine and Marine Technology Marine Nitrogen Oxide Reducing Agents AUS 40. Furthermore, the applicant also attempted to utilize the effect of nonionic surfactants on the crystallization performance of diesel exhaust fluids (Zhao Yang, Yan Feng, *Journal of Tianjin University of Technology*, June 2023), adding nonionic surfactants to urea aqueous solutions before filtration, fine filtration, and ultrafiltration. This method utilizes the adsorption of nonionic surfactants on the surface of insoluble matter to promote dispersion. While this method can reduce membrane fouling, the interactions between nonionic surfactants in the membrane contaminants lead to high viscosity, making ultrafiltration membrane rinsing difficult. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a marine nitrogen oxide reducing agent and its preparation method. This invention uses the same production equipment as automotive nitrogen oxide reducing agents to produce marine nitrogen oxide reducing agents, which reduces the likelihood of membrane fouling during production, resulting in high production efficiency, low production input costs, and low energy consumption. The prepared marine nitrogen oxide reducing agent meets the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Marine and Marine Technology - Marine Nitrogen Oxide Reducing Agents AUS 40.

[0012] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a nitrogen oxide reducing agent for ships includes: hydrolysis crystallization, dissolution, filtration, fine filtration, and ultrafiltration; The hydrolysis crystallization process involves mixing industrial urea and tertiary water, stirring at 73-75°C, performing a first cooling, adding dodecaacetylenol polyoxyethylene ether, performing a second cooling, adding a mixed urea solution at 62.5-64°C, performing a third cooling, maintaining the temperature, centrifuging, and using the collected precipitate as purified urea. In the hydrolysis crystallization, the mass ratio of industrial urea to tertiary water is 725-730:270; When adding dodecynediol polyoxyethylene ether, the amount of dodecynediol polyoxyethylene ether added is 50-60 mg / L; The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The mass ratio of industrial urea to mixed urea solution is 725-730:100-102; The first cooling process involves cooling at a rate of 0.05℃ / min for 100-110 minutes. The second cooling process involves cooling at a rate of 0.10℃ / min for 60-70 minutes. The third cooling process involves cooling at a rate of 0.2℃ / min for 100-110 minutes. When stirring at 73-75℃, the stirring speed is 280-320 rpm and the stirring time is 30-60 min; The heat preservation time is 20-30 minutes; The centrifugation speed is 3500-4000 rpm, and the centrifugation time is 10-15 min. The method for preparing the mixed urea solution is as follows: polyethylene glycol 8000, urea and tertiary water are mixed and stirred at 73-75°C to obtain a composite urea solution. In the preparation of the mixed urea solution, the mass ratio of polyethylene glycol 8000, urea, and tertiary water is 5-5.2:65-65.8:30-31. When stirring at 73-75℃, the stirring speed is 300-350 rpm and the stirring time is 30-60 min; The dissolution process involves mixing purified urea, tertiary water, and a mixed surfactant solution, and stirring at 40-45°C to obtain an aqueous urea solution. In the dissolution process, the mass ratio of purified urea, tertiary water, and mixed surfactant solution is 40:50:10. When stirring at 40-45℃, the stirring speed is 200-400 rpm and the stirring time is 30-60 min; The method for preparing the mixed surfactant solution is as follows: dodecynediol polyoxyethylene ether, anhydrous ethanol and tertiary water are mixed and stirred at 60-65°C. The stirring speed of the reaction equipment is controlled at 300-350 rpm and stirred for 30-60 min to obtain the mixed surfactant solution. In the preparation of the mixed surfactant solution, the mass ratio of dodecynediol polyoxyethylene ether, anhydrous ethanol, and tertiary water is 1-1.1:10-12:1000-1100. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; When stirring at 60-65℃, the stirring speed is 300-350 rpm and the stirring time is 30-60 min; The filtration process involves using a bag filter to filter the urea solution, resulting in a filtered urea solution. In the filtration process, the filter screen used in the bag filter is a polyethylene filter screen, and the filtration accuracy of the polyethylene filter screen is 1μm. The fine filtration is performed by using a fine filtration device to finely filter the filtered urea aqueous solution to obtain a finely filtered urea aqueous solution. In the fine filtration process, the filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm. The ultrafiltration process involves using an ultrafiltration device to ultrafilter the finely filtered urea aqueous solution to obtain a nitrogen oxide reducing agent for marine use. In the ultrafiltration process, the filter membrane used in the ultrafiltration equipment is a polysulfone filter membrane; The filter membrane used in the ultrafiltration equipment has a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25℃ and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.24-0.26 MPa; All the water in question meets the national standard GB / T 6682-2008.

[0013] A reducing agent for nitrogen oxides used in ships, prepared by the aforementioned method.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the marine nitrogen oxide reducing agent of the present invention, in the preparation process, according to the content disclosed in Zhao Yang and Yan Feng, Journal of Tianjin University of Technology, June 2023, uses nonionic surfactants to inhibit urea crystallization. However, the difference from the prior art is that the present invention adds nonionic surfactants in the hydrolysis crystallization step. According to the content disclosed in Xia Sen, Zhejiang University, April 2024, when inhibiting methionine crystallization, hydroxypropyl cellulose mainly inhibits methionine aggregation or cluster formation by adsorbing on the surface of methionine crystals and inhibiting methionine aggregation or cluster formation through steric hindrance. Hydroxypropyl cellulose has a stronger inhibitory effect on axial growth than radial growth, causing a decrease in the crystal aspect ratio. The applicant referenced this principle and added a nonionic surfactant, dodecaacetylene glycol polyoxyethylene ether, before increasing the cooling rate to inhibit seed crystal formation. Then, before further increasing the cooling rate, a mixed urea solution containing polyethylene glycol 8000 and urea was added. According to the published research in "Performance and Mechanism of NO2 Removal by Wet Washing Reduction of Polyethylene Glycol / Urea Composite Solution" by Cheng Junqi, Dalian Maritime University, June 2023, there is a binding force between polyethylene glycol and urea. The large molecular weight of polyethylene glycol 8000 leads to significant steric hindrance, further resulting in a high viscosity of the polyethylene glycol 8000 aqueous solution. Therefore, this invention first mixes polyethylene glycol 8000 with urea. The polyethylene glycol 8000 and urea are bound together by intermolecular forces to obtain a mixed urea solution. This mixed urea solution is then added to a hydrolysis crystallization system. Utilizing the interaction between polyethylene glycol 8000 and urea, it adsorbs onto the surface of urea crystals and preferentially grows radially where steric hindrance is relatively low. The pre-bound urea in polyethylene glycol 8000 promotes urea aggregation and crystal growth, thus ensuring uniform size and particle size of the urea crystals. Furthermore, the nonionic surfactant dodecynekyne glycol polyoxyethylene ether coated on the surface of the urea crystals and polyethylene glycol 8000 also have a synergistic effect, preventing urea from entraining dust. (2) The preparation method of the marine nitrogen oxide reducing agent of the present invention also includes a mixed surfactant solution. The mixed surfactant solution is composed of nonionic surfactant dodecynediol polyoxyethylene ether and anhydrous ethanol. According to the content disclosed in Xiao Danfeng, Wang Yongchang, Zhang Minghui, Zhang Chunyan. Collection of Oil Production Engineering. June 2018, there is an interaction force between ethanol and surfactant micelles. At high temperature, the thermal motion of ethanol is intensified, which can reduce the viscosity of surfactant. In the present invention, when the nonionic surfactant dodecynediol polyoxyethylene ether coats and disperses insoluble matter, a portion of ethanol is also bound. Therefore, when insoluble matter is adsorbed on the surface of ultrafiltration membrane to form membrane contaminants, some ethanol is also entrained in the membrane contaminants. At high temperature, the thermal motion of ethanol is intensified, which will reduce the concentration of membrane contaminants and contribute to the dissolution of membrane contaminants. (3) This invention uses the same production equipment as automotive nitrogen oxide reducing agents to produce marine nitrogen oxide reducing agents. The prepared marine nitrogen oxide reducing agent meets the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Marine and Marine Technology Marine Nitrogen Oxide Reducing Agents AUS 40, and its density at 20℃ is 1127-1132 kg / m³. 3 The refractive index at 20℃ is 1.3954-1.3958, alkalinity (based on NH3) is 0.12-0.13%, biuret content is 0.15-0.17%, aldehyde content is 3.1-3.5 mg / kg, insoluble matter content is 4.0-4.2 mg / kg, phosphate content is 0.22-0.24 mg / kg, calcium content is 0.12-0.13 mg / kg, iron content is 0.08-0.10 mg / kg, magnesium content is 0.13-0.15 mg / kg, sodium content is 0.08-0.09 mg / kg, and potassium content is 0.16-0.19 mg / kg. Moreover, it is not prone to membrane fouling during production, and the treatment of membrane pollutants is relatively easy. (4) The preparation method of the marine nitrogen oxide reducing agent of the present invention requires less time during hydrolysis and crystallization, and does not require heating in ultrafiltration, thus resulting in high production efficiency and low energy consumption; it does not require improvement of production equipment, thus resulting in low production input cost. Detailed Implementation

[0015] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0016] The Class III water used in Examples 1-2 and Comparative Examples 1-3 met the requirements for Class III water in the national standard GB / T 6682-2008.

[0017] The tertiary water used in Examples 1-2 and Comparative Examples 1-3 was from the same production batch and had a conductivity of 0.30 mS / m at 25°C.

[0018] The industrial urea used in Examples 1-2 and Comparative Examples 1-3 was from the same production batch, with a total nitrogen (N) content (on a dry basis) of 46.4%.

[0019] In Examples 1-2 and Comparative Examples 1-3, the density, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble matter content, phosphate content, calcium content, iron content, magnesium content, sodium content, and potassium content of the prepared marine nitrogen oxide reducing agent were tested according to the test methods specified in GB / T 35176.1-2017 / ISO 186 11-1:2014 Ships and Marine Technology Marine Nitrogen Oxide Reducing Agents AUS 40.

[0020] Example 1 A method for preparing a nitrogen oxide reducing agent for ships is as follows: Step 1: Hydrolysis and Crystallization Add 730g of industrial urea and 270g of tertiary water to the reaction equipment. Control the temperature inside the reaction equipment to 75℃ and the stirring speed to 300rpm. Stir for 30min, keeping the stirring speed constant. Cool for 100min at a cooling rate of 0.05℃ / min. Add dodecynediol polyoxyethylene ether, controlling the amount of dodecynediol polyoxyethylene ether added to be 50mg / L. Cool for 60min at a cooling rate of 0.10℃ / min. Add 100g of mixed urea solution at 64℃. Cool for 100min at a cooling rate of 0.2℃ / min. Hold at this temperature for 20min. Transfer to a centrifuge. Control the centrifugation speed to 3500rpm and centrifuge for 10min. Use the collected precipitate as purified urea. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The method for preparing the mixed urea solution is as follows: 5g of polyethylene glycol 8000, 65g of urea and 30g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 75℃, the stirring speed of the reaction equipment is controlled to 300rpm, and the mixture is stirred for 30min to obtain the composite urea solution. Step 2: Dissolve Immediately add all the purified urea obtained in step 1, along with tertiary water and a mixed surfactant solution, into the reaction apparatus. Control the mass ratio of purified urea, tertiary water, and mixed surfactant solution to 40:50:10. Control the temperature inside the reaction apparatus to 40°C. Control the stirring speed of the reaction apparatus to 200 rpm. Stir for 30 minutes to obtain a urea aqueous solution. The method for preparing the mixed surfactant solution is as follows: 1g of dodecaacetylenic diol polyoxyethylene ether, 10g of anhydrous ethanol and 1000g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 60℃, the stirring speed of the reaction equipment is controlled to 300rpm, and the mixture is stirred for 30min to obtain the mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; Step 3: Filtering The entire urea solution obtained in step 2 was filtered using a bag filter to obtain a filtered urea solution. The filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm. Step 4: Fine filtration The urea aqueous solution obtained in step 3 was further filtered using a fine filtration device to obtain a finely filtered urea aqueous solution. The filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm; Step 5: Ultrafiltration The urea aqueous solution obtained in step 4 was subjected to ultrafiltration using an ultrafiltration device to obtain a nitrogen oxide reducing agent for ships. The ultrafiltration equipment uses a polysulfone membrane with a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.25 MPa.

[0021] This embodiment also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0022] The nitrogen oxide reducing agent for ships prepared in this embodiment has a density of 1132 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3958, the alkalinity (as NH3) is 0.13%, the biuret content is 0.17%, the aldehyde content is 3.5 mg / kg, the insoluble matter content is 4.2 mg / kg, the phosphate content is 0.24 mg / kg, the calcium content is 0.12 mg / kg, the iron content is 0.10 mg / kg, the magnesium content is 0.15 mg / kg, the sodium content is 0.08 mg / kg, and the potassium content is 0.16 mg / kg.

[0023] Comparative Example 1 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that the addition of dodecaacetylenic diol polyoxyethylene ether was omitted in step 1: hydrolysis crystallization.

[0024] The remaining technical solutions are the same as in Example 1.

[0025] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0026] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1135 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3961, the alkalinity (as NH3) is 0.12%, the biuret content is 0.19%, the aldehyde content is 3.3 mg / kg, the insoluble matter content is 12.7 mg / kg, the phosphate content is 0.27 mg / kg, the calcium content is 0.11 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.17 mg / kg, the sodium content is 0.09 mg / kg, and the potassium content is 0.16 mg / kg.

[0027] Comparative Example 2 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that the addition of the mixed urea solution was omitted in step 1: hydrolysis crystallization.

[0028] The remaining technical solutions are the same as in Example 1.

[0029] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0030] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1140 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3967, the alkalinity (as NH3) is 0.13%, the biuret content is 0.19%, the aldehyde content is 3.0 mg / kg, the insoluble matter content is 8.2 mg / kg, the phosphate content is 0.23 mg / kg, the calcium content is 0.12 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.16 mg / kg, the sodium content is 0.10 mg / kg, and the potassium content is 0.15 mg / kg.

[0031] Comparative Example 3 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that in step 2: the preparation method of the mixed surfactant solution was changed to: Add 1g of dodecaacetylenic diol polyoxyethylene ether and 1000g of tertiary water to the reaction equipment, control the temperature inside the reaction equipment to 60℃, control the stirring speed of the reaction equipment to 300rpm, stir for 30min, and obtain a mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0.

[0032] The remaining technical solutions are the same as in Example 1.

[0033] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0034] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1141 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3970, the alkalinity (as NH3) is 0.15%, the biuret content is 0.20%, the aldehyde content is 3.6 mg / kg, the insoluble matter content is 4.1 mg / kg, the phosphate content is 0.27 mg / kg, the calcium content is 0.13 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.16 mg / kg, the sodium content is 0.15 mg / kg, and the potassium content is 0.20 mg / kg.

[0035] Example 2 A method for preparing a nitrogen oxide reducing agent for ships is as follows: Step 1: Hydrolysis and Crystallization Add 730g of industrial urea and 270g of tertiary water to the reaction equipment. Control the temperature inside the reaction equipment to 75℃ and the stirring speed to 300rpm. Stir for 60min, keeping the stirring speed constant. Cool for 110min at a cooling rate of 0.05℃ / min. Add dodecynediol polyoxyethylene ether, controlling the amount of dodecynediol polyoxyethylene ether added to 60mg / L. Cool for 70min at a cooling rate of 0.10℃ / min. Add 102g of mixed urea solution at 62.5℃. Cool for 110min at a cooling rate of 0.2℃ / min. Hold at this temperature for 30min. Transfer to a centrifuge and centrifuge at 4000rpm for 15min. Use the collected precipitate as purified urea. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The method for preparing the mixed urea solution is as follows: 5.2g of polyethylene glycol 8000, 65.8g of urea and 31g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 75℃, the stirring speed of the reaction equipment is controlled to 350rpm, and the mixture is stirred for 60min to obtain the composite urea solution. Step 2: Dissolve Immediately add all the purified urea obtained in step 1, along with tertiary water and a mixed surfactant solution, into the reaction apparatus. Control the mass ratio of purified urea, tertiary water, and mixed surfactant solution to 40:50:10. Control the temperature inside the reaction apparatus to 45°C and the stirring speed of the reaction apparatus to 400 rpm. Stir for 60 minutes to obtain a urea aqueous solution. The method for preparing the mixed surfactant solution is as follows: 1.1g of dodecaacetylenic diol polyoxyethylene ether, 12g of anhydrous ethanol and 1100g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 65℃, the stirring speed of the reaction equipment is controlled to 350rpm, and the mixture is stirred for 60min to obtain the mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; Step 3: Filtering The entire urea solution obtained in step 2 was filtered using a bag filter to obtain a filtered urea solution. The filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm. Step 4: Fine filtration The urea aqueous solution obtained in step 3 was further filtered using a fine filtration device to obtain a finely filtered urea aqueous solution. The filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm; Step 5: Ultrafiltration The urea aqueous solution obtained in step 4 was subjected to ultrafiltration using an ultrafiltration device to obtain a nitrogen oxide reducing agent for ships. The ultrafiltration equipment uses a polysulfone membrane with a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.25 MPa.

[0036] This embodiment also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0037] The nitrogen oxide reducing agent for ships prepared in this embodiment has a density of 1127 kg / m³ at 20°C. 3The refractive index at 20℃ is 1.3954, the alkalinity (based on NH3) is 0.12%, the biuret content is 0.15%, the aldehyde content is 3.1 mg / kg, the insoluble matter content is 4.0 mg / kg, the phosphate content is 0.22 mg / kg, the calcium content is 0.13 mg / kg, the iron content is 0.08 mg / kg, the magnesium content is 0.13 mg / kg, the sodium content is 0.10 mg / kg, and the potassium content is 0.19 mg / kg.

[0038] The density, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble content, phosphate content, calcium content, iron content, magnesium content, sodium content, and potassium content of the marine nitrogen oxide reducing agents prepared in Examples 1-2 and Comparative Examples 1-3 all comply with the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Ships and Marine Technology - Marine Nitrogen Oxide Reducing Agents AUS 40. This indicates that the preparation methods of Examples 1-2 and Comparative Examples 1-3, after adding appropriate modifiers for adjustment, will not lead to the problem of the prepared marine nitrogen oxide reducing agents failing to meet the standard requirements. However, compared with the marine nitrogen oxide reducing agent prepared in Example 1, the marine nitrogen oxide reducing agent prepared in Comparative Examples 1-2 has a relatively higher insoluble content.

[0039] Experimental Example 1 In Examples 1-2 and Comparative Examples 1-3, step 2: dissolution was modified by changing the phrase "immediately add all the purified urea obtained in step 1 to the reaction equipment with tertiary water" to "after placing all the purified urea obtained in step 1 in an open environment at a temperature of 23±1℃ and a relative humidity of 55±2% for 2 days, it was then added to the reaction equipment with tertiary water." The insoluble content of the prepared marine nitrogen oxide reducing agent was then tested, and the results are as follows:

[0040] The results above show that after the purified urea was left exposed for 1 day, the content of insoluble matter in the marine nitrogen oxide reducing agent prepared in Comparative Examples 1-2 was significantly higher than that in Example 1, indicating that the purified urea prepared in Comparative Examples 1-2 was more likely to carry dust.

[0041] Experimental Example 2 Thirty batches of marine nitrogen oxide reducing agent were continuously prepared according to the preparation methods of Examples 1-2 and Comparative Examples 1-3, respectively. Before continuous preparation, the polyethylene filter screen, polypropylene filter element, and polysulfone filter membrane were replaced with new ones. During continuous preparation, the filter screen, filter element, and filter membrane were not replaced with new ones. After continuous preparation, the stable pure water flux of the polysulfone filter membrane at 25°C and 0.1 MPa was tested. The test results are as follows:

[0042] Then, the polysulfone filter membrane was soaked in hot water at 50℃ for 40 minutes, and the stable pure water flux of the polysulfone filter membrane at 25℃ and 0.1MPa was tested. The test results are as follows:

[0043] The results above show that, compared with the preparation method of Example 1, the preparation methods of Comparative Examples 1-2 are more prone to membrane fouling. In the preparation method of Comparative Example 3, the membrane flux is more difficult to recover after membrane fouling, indicating that the adhesion of membrane pollutants is stronger.

Claims

1. A method for preparing a nitrogen oxide reducing agent for ships, characterized in that, include: Hydrolysis crystallization, dissolution, filtration, fine filtration, ultrafiltration; The hydrolysis crystallization process involves mixing industrial urea and tertiary water, stirring at 73-75°C, performing a first cooling, adding dodecaacetylenol polyoxyethylene ether, performing a second cooling, adding a mixed urea solution at 62.5-64°C, performing a third cooling, maintaining the temperature, centrifuging, and using the collected precipitate as purified urea. In the hydrolysis crystallization, the mass ratio of industrial urea to tertiary water is 725-730:270; When adding dodecynediol polyoxyethylene ether, the amount of dodecynediol polyoxyethylene ether added is 50-60 mg / L; The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The mass ratio of industrial urea to mixed urea solution is 725-730:100-102; The first cooling process involves cooling at a rate of 0.05℃ / min for 100-110 minutes. The second cooling process involves cooling at a rate of 0.10℃ / min for 60-70 minutes. The third cooling process involves cooling at a rate of 0.2℃ / min for 100-110 minutes. The method for preparing the mixed urea solution is as follows: polyethylene glycol 8000, urea and tertiary water are mixed and stirred at 73-75°C to obtain the mixed urea solution. In the preparation of the mixed urea solution, the mass ratio of polyethylene glycol 8000, urea, and tertiary water is 5-5.2:65-65.8:30-31. The dissolution process involves mixing purified urea, tertiary water, and a mixed surfactant solution, and stirring at 40-45°C to obtain an aqueous urea solution. The method for preparing the mixed surfactant solution is as follows: dodecynediol polyoxyethylene ether, anhydrous ethanol and tertiary water are mixed and stirred at 60-65°C to obtain the mixed surfactant solution.

2. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, During the hydrolysis crystallization, the centrifugation speed is 3500-4000 rpm and the centrifugation time is 10-15 min.

3. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the dissolution process, the mass ratio of purified urea, tertiary water, and mixed surfactant solution is 40:50:

10.

4. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the preparation of the mixed surfactant solution, the mass ratio of dodecynediol polyoxyethylene ether, anhydrous ethanol, and tertiary water is 1-1.1:10-12:1000-1100. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0.

5. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The filtration process involves using a bag filter to filter the urea solution, resulting in a filtered urea solution. In the filtration process, the filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm.

6. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The fine filtration is performed by using a fine filtration device to finely filter the filtered urea aqueous solution to obtain a finely filtered urea aqueous solution. In the fine filtration process, the filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm.

7. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The ultrafiltration process involves using an ultrafiltration device to ultrafilter the finely filtered urea aqueous solution to obtain a nitrogen oxide reducing agent for marine use. In the ultrafiltration process, the filter membrane used in the ultrafiltration equipment is a polysulfone filter membrane; The filter membrane used in the ultrafiltration equipment has a filtration accuracy of 0.01 μm; The filter membrane used in the ultrafiltration equipment has a stable pure water flux of 100 L / (m³) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.24-0.26 MPa.

8. A marine nitrogen oxide reducing agent prepared by the preparation method according to any one of claims 1-7.

Images